This invention relates to tracer heads for tracer control systems. In a typical tracer control system, a tracer head supporting a stylus is moved relative to the edge of a fixed template upon which the stylus bears. The tracer head may be fixed relative to a tool which moves with it to machine a workpiece fixed relative to the template.
The stylus bearing upon the template edge is assumed to be deflected away from the template edge normal thereto. In other words, the stylus deflection is assumed to be perpendicular to a tangent to the template edge at the point where the stylus bears upon the template. Typically, tracer control systems convert the tracer deflection into x and y deflection signals which are proportional to the components of the deflection vector. These signals are used to control the x-y drive that moves the tracer head relative to the template. (See U.S. Pat. No. 2,839,733).
Briefly according to this invention there is provided a tracer head comprising a base adapted to be mounted to an x-y drive. A frame extends from the base upon which are mounted two perpendicular differential transformers. A stylus is mounted to the base and extends away therefrom through the differential transformers. A deflection of the unfastened end of the stylus as it bears upon the template will change the output of the differential transformers. According to this invention, the stylus comprises an elongate solid cylindrical rod having, near its base, an integral flared skirt, which skirt has a smooth and consistent tangency with the cylindrical wall of the stylus. The skirt comprises an integral 360.degree. restoring spring for returning the stylus after deflection to its null position.
According to preferred embodiments, the ratio of the diameter of the base of the skirt to the diameter of the rod of the stylus is between 4:1 and 1.5:1, and the ratio of the diameter of the base to the axial distance between the base and the point of tangency is between 1:0.75 and 1:2. It is preferred that the rod is made of a magnetic chrome vanadium steel or 416 stainless steel. The standard composition of 416 stainless steel is 0.15 maximum percent by weight carbon, 1.25 percent manganese, 1 percent silicon, 12 to 14 percent chromium, 0.15 minimum percent sulfur, 0.06 maximum percent phosphorus and ramainder iron. See page 409 of Metals Handbook Volume 1, 8th Edition (1961) published by The American Society of Metals. It is yet another preferred feature of this invention that the stylus has a ball bearing mounted rotary tip rotatable upon the axis aligned with the axis of the stylus, which tip bears upon the template edge. It is yet another preferred feature of this invention that the differential transformers have E-shaped cores with one transformer coil mounted on the center leg and coils of the the opposed transformer, i.e., the differential transformer mounted on the outside legs of the core.